As communication schemes achieving an improvement in communication performance, there have been known an LTE (Long Term Evolution) system, an XGP (eXtended Global Platform) system, and a WiMAX (Worldwide Interoperability for Microwave Access) (registered trademark) system.
Conventionally, as a technique for improving a communication service in such systems, a MIMO (Multiple Input Multiple Output) technology has been proposed.
The MIMO technology is a technology that, by combining a plurality of transmission antennas and a plurality of reception antennas, forms a plurality of channels (communication channels) between transmission and reception. As an example of the MIMO technology, a communication apparatus on a transmission side (for example, a base station), by using the same radio resource, transmits a plurality of signals respectively having different data from a plurality of transmission antennas. Then, a communication apparatus on a reception side (for example, a communication terminal) receives the plurality of signals by using a plurality of reception antennas, separates the signals, and extracts the data.
In recent years, in addition to the communication schemes described above, application of SDMA (Space Division Multiple Access) (or MIMO-SDMA) has been considered or put into practical use (for example, see PLT 1 set forth below).
In a system applying the SDMA, for example, a base station serving as the communication apparatus assigns the same carrier (in the same frequency band) in the same time slot, i.e., the same radio resource to a plurality of communication terminals. In this system, in order to prevent interference between signals transmitted in the same radio resource, an adaptive array technique, for example, is employed. The base station, by performing beam control (beam forming) and null control (null steering) of the adaptive array technique, may transmit the signal to a communication terminal of interest alone. Also, the base station, when receiving a plurality of signals transmitted in the same radio resource from a plurality of communication terminals, may extract a signal from the communication terminal of interest. Since a plurality of communication terminals may use the same radio resource, utilization efficiency of the radio resource is improved.